| Cucumber (Cucumis sativus L.) is an important crop belonging to Cucurbitaceae, widely cultivated in China and the world. Cucumber has some characteristics, such as high yield, nutrient-rich and cost-effective. It is not only as raw, cooked, pickled vegetables, but also as fresh fruit. The unique flavor is one of the important characteristics of cucumber, and, on the one hand, it depends on the flavor quality such as sugar, Vc, organic acids, tannins and so on, on the other hand, it is closely related to the aromatic substances.Enhancing flavor of cucumber is one of important goals in cucumber breeding and production. However, the flavor is one of quality characters which is not easy to be studied. At present, the research of flavor substances limited to determination method, material composition, the effects of cultivation conditions, and so on. Little were known about the genetic and metabolic mechanism of cucumber flavor substances.In this study, based on preparatory work of the selection and evaluation of flavor traits in cucumber, and according to diallel-cross method, genetic effects of five kinds of sugar and aromatic substances, organic acid and soluble solids of cucumber were analyzed by using a genetic model including additive-dominance effects and their interaction effects with environments; Genetic analysis for the content of fructose,2E,6Z-nondienal and tannins in cucumber fruit has been carried out with the method of quantitative traits heredity mode by using of the mixed major gene and polygene inheritance model in different cultivation environments; 2E,6Z-nonadienal contents of 8 cucumber lines were evaluated, and EP326 with high 2E, 6Z-nonadienal content and DE843 with low 2E,6Z-nonadienal content were selected. The 2E, 6Z-nonadienal contents of EP326 and DE843 during the fruit development and the corresponding 9-LQX gene expressions were analyzed. The main conclusions are as follows:1. Five major kinds of sugar, organic acid and soluble solids contents of six parental lines and their 15 FIs were analyzed under two environments. The results presented that the performance of quality characters of cucumber were different under two environments, and it indicated there might be genotype and environment interaction in cucumber. Genetic variance indicated that the content of fructose, acid and soluble solids were mainly controlled by additive effects. By the heritability analysis, we found that there was extremely significant general heritability in the narrow sense of fructose, organic acid and soluble solids. The genotype and phenotype correlation values of the content of fructose and glucose, sucrose, maltose were positive and significant or extremely significant.2. Six parents (EP326, Xiu yan, Ri jiecheng, Xian feng, DE843 and Burpee) and fifteen F1 hybrids under two environments were used for the analysis of the genetics of aromatic substances of cucumber by genetic models including additive-dominance effects and their interaction effects with environments. The results showed that 2E-nonenal, octanol and 2E, 6Z-nondienal of cucumber were controlled by both additive and dominant effects and, nonanal and 6Z-nonenal were mainly controlled by the additive effect. The additivex environment interaction effects of 2E,6Z-nondienal were best significant. Both general heritability of narrow sense and general heritability of broad sense of five aromatic substances were significant at 1% level probability, it indicated that the selection might be more effective in early generations. The extremely significant genetic correlation existed among the five aromatic substances in cucumber. And predicted F1 heterosis genetic performance of the five kinds of aromatic substances under two environments in part of the combinations.3. Six generations of P, P2, F1,, BC1, BC2 and F2 from the cross of cucumber cultivar EP326 and DE843 were employed to analyze the genetic effects of the characteristic aromatic substance 2E,6Z-nondienal by using of the mixed major gene and polygene inheritance model B-1 model, the additive-dominance-epistasis genetic model, which was controlled by two pairs of major genes, was the best one for genetic analysis of the characteristic aromatic substance 2E, 6Z-nondienal in cucumber. The genetics of the characteristic aromatic substance 2E, 6Z-nondienal in cucumber could be explained mainly by additive effects. Therefore, the strategy of cross breeding could be effective for increasing the characteristic aromatic substance 2E, 6Z-nondienal content of cucumber.4. Six generations (P1, P2, F1,BC1,BC2 and F2) derived from the cross of EP326*KL-2, produced under two different growing environments, were used as genetic populations to study the inheritance of fructose content by the mixed major-gene plus polygene inheritance mode with joint analysis method of multiple generations. The result showed that the fructose content of cucumber was controlled by one additive-dominance major genes plus additive-dominant polygene, and also affected by environment. In the quality breeding program, the selection for the fructose content should be carried out on high separated generations.5. Six generations (P1, P2, F1, B1, B2 and F2) derived from the cross of DE843×EP326, produced under two different growing environments, were used as genetic populations to study the inheritance of tannin content by the mixed major-gene plus polygene inheritance mode with joint analysis method of multiple generations. The result showed that the tannin content of cucumber was controlled by two pairs of additive-dominance major genes plus additive-dominant polygene, and also affected by environment. In the quality breeding program, the selection efficiency to major gene of the F2 is the highest.6.2E,6Z-nonadienal contents of 8 cucumber lines were evaluated, and EP326 with high 2E, 6Z-nonadienal content and DE843 with low 2E,6Z-nonadienal content were selected. The results indicated that 2E,6Z-nonadienal content reached the highest levels at the 9th day and 12th after pollination in EP326 and DE843, respectively.7. Five 9-LOX family gene expression results indicated that Csa007837 was mainly expressed in pulp, and the gene expressions of Csa007837 was similar with 2E,6Z-nonadienal content during the fruit development in EP326 and DE843. However, the gene expression of Csa007837 in EP326 was higher than in DE843. The correlation analysis suggested that Csa007837 was positive correlated with 2E,6Z-nonadienal content, the other four 9-LOX genes showed no correlation with 2E,6Z-nonadienal contents. Therefore, Csa007837(9-LOX) may play a key role in the process formed aroma substance in cucumber fruit. |
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